The knowledge of how individual genes are regulated and how individual gene products alter cellular metabolism is central to an understanding of how the growth of eukaryotic cells is controlled, and how this control may be lost in oncogenic transformation. The long term objectives of my studies are to genetically analyze the structure and function of eukaryotic enhancer elements and biochemically analyze in detail the factors that interact with these sequences. Enhancers are key regulatory sequences that control viral and cellular gene expression. A prime example of the importance of these elements is the finding that enhancer/promoter insertion upstream of cellular oncogenes can lead to tumorigenesis in vivo. The subject of this proposal is our work with the polyomavirus enhancer region. The polyoma enhancer is particularly interesting because this region regulates viral transcription in a developmentally specific fashion, and also is required for efficient viral DNA replication as well as transcription. In this proposal, we describe the identification of a nuclear factor, present in undifferentiated and differentiated mouse and human cells, that specifically binds to a polyoma enhancer element. We believe that we have identified a new eukaryotic enhancer binding protein. The goals of this proposal are: 1) to genetically analyze the function of this polyoma enhancer region in the regulation of transcription and DNA replication in vivo, 2) to purify the protein that binds to this enhancer region to analyze the binding of this factor to wild type and mutant enhancer domains to directly correlate in vivo enhancer function with in vitro factor binding activity and, 3) to generate monoclonal antibodies against this product that will be used to characterize this protein in detail biochemically and for subsequent purification of this enhancer binding factor.